We have identified a family with autosomal recessive disease affecting estrogen receptor expression and function. The homozygote proband is an adult male with markedly decreased bone mineral density. This study will examine (1) whether there is a relationship between estrogen receptor status in this patient's pedigree; and (2) study the inheritance of this mutation. We hypothesize that carriers of this mutation will have decreased BMD and alterations in biomarkers of bone metabolism consistent with increased bone turnover.